This invention relates to gas turbine engines, such as those used in aircraft or in utility power plants. The invention provides an economical method of determining the concentration of a component of the exhaust gas of the engine, based on measurements taken at a single point probe, located well upstream of the exhaust stack, such as in one combustor of the engine.
A gas turbine engine, such as that used in an aircraft or a utility power plant, includes a compressor, a combustion section, and a turbine. Typically, the combustion section includes a plurality of separate combustors, arranged in a circle around a central axis so that the combustors act in parallel. The combustors are sometimes called "cans", and the arrangement is referred to as can-annular.
In the design of turbine engines, an important criterion is the level of emissions of various combustion products, especially NOx and carbon monoxide (CO). When the structure of a combustor is proposed to be modified, it is necessary to know how much NOx and/or CO will be emitted by an engine built with combustors having the modified design.
While some properties of the modified combustor, such as its temperature, can be measured directly, measurement of emissions presents a problem. A gas turbine engine typically has many combustors, sometimes as many as eighteen or twenty. A change in only one combustor will have a very small effect on the emissions of the entire engine, and this change is not usually large enough to measure accurately when masked by the contributions of all the others. Thus, in the prior art, in order to determine the concentration of NOx and/or CO in the exhaust of a modified engine, it was considered necessary to build a prototype of the complete engine, including all of its combustors, and to take actual measurements of exhaust products at a location where the exhaust gases are considered well mixed and completely uniform. This procedure is time-consuming and expensive, because it requires that one build and install a full complement of duplicate copies of a redesigned combustor, without knowing beforehand how well the combustor will work.
The present invention solves the above-described problem, by providing a method of determining the concentration of an exhaust component of an engine, which method requires measurements to be taken at only one of the combustors of the engine. Therefore, the present invention eliminates the need to build multiple prototypes when developing a new combustor. The invention also provides a diagnostic method and apparatus for monitoring the performance of an engine, and for taking action when the performance of one of its combustors deteriorates.